Sagittal balance (C7 plumb line)

Sagittal balance forms part of the plain radiographic assessment of spinal deformity including kyphotic or lordotic deformities and scoliosis. There are numerous ways of assessing this, using various bony landmarks and angles to evaluate whether or not a normal distribution of weight and stresses is present through the axial skeleton 1,2. Individuals with abnormal sagittal balance are at risk of progressive spinal deformity and pain.

C7 plumb line

One of the simplest and widely used methods is performed on lateral standing full-length films and requires a vertical line (plumb line) drawn from the middle of the body of the C7 vertebral body. This line should pass through the superior endplate of S1, or more precisely within 2 cm (some use 1.7 cm) of the posterosuperior corner of the S1 vertebral body 1,2. The position of this line is then termed positive, neutral or negative:

positive balance: the plumb line passes more than 2 cm in front of the posterosuperior corner of the S1 vertebral body

neutral balance: the plumb line passes within 2 cm of the posterosuperior corner of the S1 vertebral body

negative balance: the plumb line passes more than 2 cm behind the posterosuperior corner of the S1 vertebral body

Numerous other methods for assessing sagittal balance, some incorporating the position of the head, while others focusing on the pelvis, have been described. These include 2:

2. Roussouly P, Nnadi C. Sagittal plane deformity: an overview of interpretation and management. European spine journal : official publication of the European Spine Society, the European Spinal Deformity Society, and the European Section of the Cervical Spine Research Society. 19 (11): 1824-36. doi:10.1007/s00586-010-1476-9 - Pubmed